Edge Function 503 error response

A 503 HTTP status code from an Edge Function indicates one of three possible events:

  • the function failed to boot due to SyntaxError
  • your own code returned a 503
  • the platform itself is having issues

These require different fixes, so it is useful to decipher the cause before debugging:

Step 1: Figure out which 503 you have

If you received back a BOOT_ERROR message, like the one below, you can jump to the resolution section: Boot Error

{
  "code": "BOOT_ERROR",
  "message": "Function failed to start (please check logs)"
}

Otherwise, run the below query in the SQL Editor.

select
  log_attributes['request.pathname'] as function_name,
  log_attributes['response.status_code'] as status_code,
  case
    when log_attributes['execution_id'] != ''
    and log_attributes['function_id'] != '' then 'app_level'
    when log_attributes['execution_id'] = ''
    and log_attributes['function_id'] != '' then 'boot_error'
    when log_attributes['execution_id'] = ''
    and log_attributes['function_id'] = '' then 'internal_failure'
  end as error_type
from logs
where
  source = 'function_edge_logs'
  and toInt32OrZero(log_attributes['response.status_code']) = 503
limit 50;

Depending on the output, you can use this table to find the appropriate debugging section:

Value Go to
app_level app level error
boot_error boot error - function cannot compile
internal_failure platform issue

Step 2: Addressing the error

App level error

Somewhere in your function logic, you are returning a 503 response yourself:

Example:

return new Response(JSON.stringify(data), {
  headers: { ...corsHeaders, 'Content-Type': 'application/json' },
  status: 503, // <-- you set this
})

Check your function logic and any third-party API responses for where the 503 is originating.

  1. Search your function code for 503. Look for explicit status codes on Response objects
  2. Trace the condition that triggered it. If your function calls external APIs, it may be passing along errors returned by those services
  3. Add logging before the return so future occurrences leave a trace:
console.error('Returning 503 - reason:', reason)

See: Error handling in Edge Functions

Boot error

A SyntaxError prevented your code from dynamically compiling.

In the Function Dashboard, under the affected function’s Log tab, you can filter for the key phrase worker boot error:. the log will tell you syntax error occurred:

image

Alternatively, instead of using the Function Dashboard, you can programmatically find boot failure error messages in the SQL Editor with the below query:

select
  fl.event_message,
  fl.timestamp,
  fel.function_name,
  fel.status_code
from
  (
    select
      timestamp,
      event_message,
      log_attributes['function_id'] as function_id,
      log_attributes['version'] as version
    from logs
    where source = 'function_logs'
      and log_attributes['event_type'] = 'BootFailure'
  ) as fl
  left join (
    select
      log_attributes['function_id'] as function_id,
      log_attributes['version'] as version,
      log_attributes['request.pathname'] as function_name,
      log_attributes['response.status_code'] as status_code
    from logs
    where source = 'function_edge_logs'
  ) as fel on fl.function_id = fel.function_id and fl.version = fel.version
order by fl.timestamp, fel.function_name
limit 20;

Example causes

Redefining constant variables

Redefining a constant value can prevent the code from compiling:

let some_var
const some_var // SyntaxError — already declared

The log message for these errors should state the cause already declared and the file impacted.

worker boot error: Uncaught SyntaxError:
Identifier 'some_var' has already been declared at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:6:7

Key word violations

Some key words can only be used in specific contexts. For instance, the await key word can only be used inside async functions.

(req: Request) => {
  const { name } = await req.json(); // await only works inside async functions
}

The log message for these errors should state the cause Unexpected reserved word and the file impacted.

worker boot error: Uncaught SyntaxError:
Unexpected reserved word at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:6:28

Bad imports: Non-existent modules or named exports

Imports can cause errors if they’re not available within the edge function:

// importing non-existent module
import supabase from 'does_not_exist'
// or accessing non-existent export
import { doesNotExist } from 'jsr:@supabase/functions-js'

doesNotExist()

The log message for these errors should state the cause requested module... does not provide an export and the file impacted.

worker boot error: Uncaught SyntaxError:
The requested module 'jsr:@supabase/functions-js' does not provide an export named 'doesNotExist' at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:2:10”

To fix, check the module and its imports to make sure they exist and are supported by Supabase Edge Functions.

If the module worked before, check to see if the most recent release had breaking changes and then only import the working version.

Platform issue

The edge function runtime is overwhelmed, or the API Gateway is returning its own 503 due to excessive load.

Open a support ticket and include the relevant log output from Step 1.

Additional resources

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